The major goal of this work is to determine how the acid-secreting parietal cells of the rabbit stomach maintain ionic homeostasis during large changes in their secretory activity. Microspectrofluorimetry and digital image processing of pH-, Na- Ca-, Cl- and K-sensitive fluorescent dyes will be used to determine how the ion exchangers (Na/H, Cl/HCO3, and Na/Ca), cotransporter (Na/HCO3), ATP-ases (Na/K and H/K), and Ca "channels" are controlled by the H2 agonist histamine and muscarinic agonist carbachol. The roles which different second messengers like Ca, pH, CAMP and protein kinase C may play in stimulus secretion coupling will also be investigated, as will the roles which Na/H and Cl/HC03 exchange might play in maintenance of the "barrier" function of the enzyme-secreting chief cells and mucus-secreting surface epithelial cells. These data will be of importance in knowing how stomach cells operate in healthy and diseased states. Also, since the membrane transport processes and stimulus-secretion coupling mechanisms are present in most secretory cells, the work should have quite broad relevance.